Tunable pressure transducer assembly

ABSTRACT

A tunable pressure transducer assembly that comprises a sensing element disposed within a housing, wherein the sensing element is adapted to output a signal substantially indicative of an applied pressure, and a filter assembly also disposed within the housing. The filter assembly comprises a cap and a tube, wherein the cap is spaced from the sensing element within the housing such that it encloses a set volume around the sensing element, and wherein the tube controls access of the applied pressure to the set volume. The filter assembly is operative to substantially reduce high frequency pressure ripples and allow static and quasi-static pressures to pass through to the sensing element, and may be manipulated to tune the pressure transducer assembly to achieve a desired dampening frequency. The filter assembly therefore enables one pressure transducer assembly outline to accurately measure pressure in various systems.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. §119(e) to U.S.Provisional Application 61/381,734, entitled “Method of Tuning InputFrequency Response of a Pressure Transducer,” filed Sep. 10, 2010. Thisapplication is hereby incorporated by reference as if fully set forthherein.

BACKGROUND

Pressure transducer assemblies used to measure pressure in varioussystems, for example, gas turbine engines, are adversely impacted bypressure ripples often caused by pumping equipment. If high frequencypressure ripples are applied near a resonance frequency of the pressuretransducer, either from an internal cavity or a mechanical structure,the pressure ripples can negatively impact and shorten the lifeexpectancy of the pressure transducer. One way to avoid this undesirablesituation is to design a pressure transducer that has minimal or noresonances near the frequency of the ripple. This can, however, becostly and time consuming as pressure ripple frequencies can change fromsystem to system. Therefore, different pressure transducers must bedesigned for each unique system.

In some cases, it is not desirable to measure the pressure ripple of asystem. Instead, only steady state pressure level measurements aredesired. In these cases, a filter assembly may be placed at the frontend of the transducer to eliminate the higher frequency ripples andleave static and quasi-static pressures intact. Many embodiments of theprior art utilize a filter assembly specifically designed for eachindividual system to be measured, which can be very costly as the filterassemblies are not equipped to adapt to various systems.

Thus, there is a need for a pressure transducer assembly that comprisesa tunable filter assembly that can adapt to multiple systems andapplications, which therefore reduces costs associated with designingindividual filters for individual systems and applications.

BRIEF SUMMARY

The various embodiments of the present invention provide a tunablepressure transducer assembly that comprises a sensing element disposedwithin a housing, wherein the sensing element is adapted to output asignal substantially indicative of an applied pressure, and a filterassembly also disposed within the housing. The filter assembly comprisesa cap and a tube, wherein the cap is spaced from the sensing elementwithin the housing such that it encloses a set volume around the sensingelement, and wherein the tube controls access of the applied pressure tothe set volume. The filter assembly is operative to substantially reducehigh frequency pressure ripples and allow static and quasi-staticpressures to pass through to the sensing element, and may be manipulatedto tune the pressure transducer assembly to achieve a desired dampeningfrequency. The filter assembly therefore enables one pressure transducerassembly outline to be tunable for measuring pressure in many differentsystems.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates an embodiment of a tunable pressure transducerassembly in accordance with exemplary embodiments of the presentinvention.

DETAILED DESCRIPTION

Although preferred embodiments of the invention are explained in detail,it is to be understood that other embodiments are contemplated.Accordingly, it is not intended that the invention is limited in itsscope to the details of construction and arrangement of components setforth in the following description or illustrated in the drawings. Theinvention is capable of other embodiments and of being practiced orcarried out in various ways. Also, in describing the preferredembodiments, specific terminology will be resorted to for the sake ofclarity.

It must also be noted that, as used in the specification and theappended claims, the singular forms “a,” “an,” and “the” include pluralreferents unless the context clearly dictates otherwise.

Also, in describing the preferred embodiments, terminology will beresorted to for the sake of clarity. It is intended that each termcontemplates its broadest meaning as understood by those skilled in theart and includes all technical equivalents which operate in a similarmanner to accomplish a similar purpose.

Ranges may be expressed herein as from “about” or “approximately” oneparticular value and/or to “about” or “approximately” another particularvalue. When such a range is expressed, another embodiment includes fromthe one particular value and/or to the other particular value.

By “comprising” or “containing” or “including” is meant that at leastthe named compound, element, particle, or method step is present in thecomposition or article or method, but does not exclude the presence ofother compounds, materials, particles, method steps, even if the othersuch compounds, material, particles, method steps have the same functionas what is named.

Referring now to the drawings, in which like numerals represent likeelements, exemplary embodiments of the present invention are hereindescribed. It is to be understood that the figures and descriptions ofthe present invention have been simplified to illustrate elements thatare relevant for a clear understanding of the present invention, whileeliminating, for purposes of clarity, many other elements found intypical pressure transducer assemblies and methods of making and usingthe same. Those of ordinary skill in the art will recognize that otherelements are desirable and/or required in order to implement the presentinvention. However, because such elements are well known in the art, andbecause they do not facilitate a better understanding of the presentinvention, a discussion of such elements is not provided herein.

Exemplary embodiments of the present invention provide a tunablepressure transducer assembly that utilizes a filter assembly adapted totune the pressure transducer assembly to a desired attenuation frequencyto avoid resonant conditions. Therefore, several pressure transducerassemblies having the same outline can be manufactured, and eachassembly can be subsequently tuned to a desired system, thereby reducingcosts associated with designing one unique pressure transducer assemblyfor one unique system. As illustrated in FIG. 1, the pressure transducerassembly 100 comprises a housing 105 having a first end 115 and a secondend 120. A sensing element 110 mounted on a header 145 is disposedwithin the second end 120 of the housing 105. The housing 105 surroundsthe sensing element 110 and therefore protects the sensing element 110from harsh external environments. In exemplary embodiments, the sensingelement 110 is a piezoresistive sensing element that comprises fourpiezoresistors. As designed, the sensing element 110 measures an appliedpressure media and outputs a signal substantially indicative of theapplied pressure media. One skilled in the art will appreciate that thehousing 105 can be customized to fit many configurations, for examplebut not limited to, O-ring seals and threads.

A filter assembly comprising a cap 125 and a tube 130 is also disposedwithin the housing 105. The cap 125 encloses a set volume 135 around thesensing element 110 near the second end 120 of the housing 105. The tube130 fits within a channel 140 defined within the housing 105 and extendsfrom the first end 115 of the housing 105 to the cap 125, such that itis adjacent and detachably attached to the cap 125.

An incoming pressure media is applied to the first end 115 of thehousing 105 and received by the channel 140 defined within the housing105 and the tube 130. The pressure media flows through the tube 130 andthus, the tube 130 may control access of the pressure media to the cap125 and into the set volume 135. The flow and frequency of the pressuremedia may be restricted by changing the dimensions of the tube 130 andcap 125 (and, consequently the area of the set volume 135). Therefore,the cap 125 and tube 130, in combination, may act as a low passmechanical filter.

As described, the pressure transducer assembly 100 may be tuned toachieve a desired attenuation frequency. Those skilled in the art willappreciate that certain pressure media comprise high frequency pressureripples that interfere with the accuracy of the sensing element andshorten its operable lifespan. The pressure transducer assembly of thepresent invention may be tuned via the filter assembly to eliminateundesirable high frequency ripples and pass through desirable static andquasi-static pressures. Specifically, dependent on the properties of thepressure media to be measured, such as its viscosity, the length anddiameter of the cap 125 and tube 130 may be adjusted to achieve desireddampening parameters. While the diameters of the cap 125 and tube 130may fluctuate, in exemplary embodiments, the diameters of the cap 125and the tube 130 remain fixed across many different systems. Asillustrated in FIG. 1, the diameter of the tube 130 is smaller than thediameter of the cap 125 to effectively attenuate high frequency ripples.

One skilled in the art will appreciate that narrowing the tube 130(i.e., decreasing the diameter) enhances attenuation. However, if thetube 130 is too narrow for the applied pressure media, desirable lowfrequency components (e.g., static and quasi-static pressures) may alsobe eliminated, which interferes with the accuracy of the sensing element105. Conversely, if the tube 130 is too wide, high frequency ripples maynot sufficiently eliminated, which also interferes with the accuracy ofthe sensing element 105 and decreases it operable lifespan.

Further, by varying only the length of the tube 130 and the cap 125, onesingle pressure transducer assembly design may be tuned to manydifferent systems having varying pressure media properties. The actuallength of the tube 130 and cap 125 can be changed, or, and morepreferably, the length of the tube 130 and the set volume 135 via thecap 125 may be adjusted by sliding the filter assembly within thepressure transducer assembly 100. For example, to “shorten” the filterassembly, the tube 130 can be pushed towards the second end 120 of thepressure transducer assembly 100, which consequently pushes the cap 125closer to the sensing element 110 and reduces the area of the set volume135 around the sensing element 135. It is important to note thatshortening the tube 130 exposes the pressure media to more of thechannel 140 defined within the housing 105, however the channel 140 hasminimal influence on the overall frequency response.

Conversely, to “lengthen” the filter assembly, the tube 130 can bepulled away from the second end 120 of the pressure transducer assembly100 towards the first end 115 of the pressure transducer assembly, whichconsequently moves the cap 125 further away from the sensing element 110and increases the area of the set volume 130 around the sensing element125. Because the filter assembly can slide within the pressuretransducer assembly to vary the filter properties, several pressuretransducer assemblies having the same outline can be manufactured, andeach assembly can be subsequently tuned to a desired system, therebyreducing costs associated with designing one unique pressure transducerassembly for one unique system. Once the desired tuning is achieved, thefilter assembly may be fixed within the housing 105 using, for example,standard welding techniques.

Those skilled in art will appreciate that the equation below shows thewave equation for the flow of pressure through a pipe. The dampingcoefficient,

${K\frac{32\; \mu}{\rho \; D^{2}}},$

is dependent on both pipe diameter (D) and viscosity (μ).

${\frac{1}{c^{2}}\left( {\frac{\partial^{2}P^{\prime}}{\partial t^{2}} + {K\frac{32\; \mu}{\rho \; D^{2}}\frac{\partial P^{\prime}}{\partial t}}} \right)} = \frac{\partial^{2}P^{\prime}}{\partial x^{2}}$

As the equation illustrates, when the flow is in a tube 130 having asmaller diameter, the damping is increased due to its narrow diameterand long length. As the flow reaches the cap 125 and the set volume 135,the flow is further damped as it expands to fulfill the diameter of thecap 125 and the area of set volume 135. By manipulating the length ofthe tube 130 and area of the set volume 135, by moving the cap closer orfurther from the sensing element 110, the damping ratio and cut-offfrequency can be well tuned for the respective application. In this way,undesired ripple frequency can be substantially or completelyeliminated, while still retaining lower frequency components that aredesirable to measure.

Numerous characteristics and advantages have been set forth in theforegoing description, together with details of structure and function.While the invention has been disclosed in several forms, it will beapparent to those skilled in the art that many modifications, additions,and deletions, especially in matters of shape, size, and arrangement ofparts, can be made therein without departing from the spirit and scopeof the invention and its equivalents as set forth in the followingclaims. Therefore, other modifications or embodiments as may besuggested by the teachings herein are particularly reserved as they fallwithin the breadth and scope of the claims here appended.

What is claimed is:
 1. A tunable pressure transducer assembly havingvariable filter properties, comprising: a sensing element disposedwithin a housing and adapted to output a signal substantially indicativeof an applied pressure; and a filter assembly within the housing,comprising a cap and a tube, wherein the cap is spaced from the sensingelement within the housing such that it encloses a set volume around thesensing element, and wherein the tube controls access of the appliedpressure to the set volume.
 2. The assembly of claim 1, wherein thefilter assembly is slideably disposed within the housing.
 3. Theassembly of claim 2, wherein the filter assembly slides within thehousing to tune the pressure transducer assembly to a desired dampeningfrequency.
 4. The assembly of claim 1, wherein the cap is of a firstdiameter and the tube is of a second diameter, wherein the firstdiameter is greater than the second diameter.
 5. The assembly of claim1, wherein the tube is of a first length that can be changed tomanipulate the filter properties of the pressure transducer assembly. 6.The assembly of claim 1, wherein the set volume is of an area that canbe changed relative to the sensing element via the cap to manipulate thefilter properties of the pressure transducer assembly.
 7. The assemblyof claim 1, wherein the filter assembly is operative to substantiallyreduce high frequency pressure ripples and allow static and quasi-staticpressures to pass through to the sensing element.
 8. The assembly ofclaim 1, wherein the sensing element is a piezoresistive sensingelement.
 9. A tunable pressure transducer assembly, comprising: asensing element disposed within a first end of a housing and adapted tooutput a signal substantially indicative of a pressure media; and aslideable filter assembly within the housing, wherein the slideablefilter assembly is adapted to tune the pressure transducer assembly to adesired dampening frequency.
 10. The assembly of claim 9, wherein theslideable filter assembly comprises a tube and a cap, wherein the capencloses a set volume around the sensing element, and wherein the tubecontrols access of the pressure media into the set volume.
 11. Theassembly of claim 10, wherein the cap is of a first diameter and thetube is of a second diameter, wherein the first diameter is greater thanthe second diameter.
 12. The assembly of claim 10, wherein the tube isof a first length that can be changed to manipulate the filterproperties of the pressure transducer assembly.
 13. The assembly ofclaim 10, wherein the set volume is of an area that can be changedrelative to the sensing element via the cap to manipulate the filterproperties of the pressure transducer assembly.
 14. The assembly ofclaim 9, wherein the slideable filter assembly tunes the pressuretransducer assembly by providing variable positioning of the sensingelement within the set volume relative to the filter assembly.
 15. Theassembly of claim 9, wherein the filter assembly is operative tosubstantially reduce high frequency pressure ripples and allow staticand quasi-static pressures to pass through to the sensing element.
 16. Atunable pressure transducer assembly, comprising: a housing having afirst end and a second end, wherein a channel is defined within thehousing and extends a length of the first end, and wherein a set volumeis defined within the second end of the housing; a filter assemblyhaving a tube and a cap, wherein the tube is disposed in the channel andthe cap is disposed in at least a portion of the set volume; a header,comprising a pressure sensing element, mounted in the set volumeopposite the cap; wherein the cap encloses the set volume around thesensing element; and wherein the filter assembly is adapted to slidewithin the housing to tune the pressure transducer assembly to a desireddampening frequency.
 17. The assembly of claim 16, wherein the channelis of a first diameter and the set volume is of a second diameter, andwherein the first diameter is smaller than the second diameter.
 18. Theassembly of claim 16, wherein the cap is of a first diameter and thetube is of a second diameter, wherein the first diameter is greater thanthe second diameter.
 19. The assembly of claim 16, wherein the tube isof a first length that can be changed to manipulate filter properties ofthe pressure transducer assembly.
 20. The assembly of claim 16, whereinthe set volume around the sensing element is of an area that can bechanged relative to the sensing element via the cap to manipulate filterproperties of the pressure transducer assembly.
 21. A method of making atunable pressure transducer assembly, comprising: providing a housinghaving a first end and a second end, wherein a channel is definedtherein and extends the length of the first end, and further wherein acavity is defined within the second end of the housing; disposing afilter assembly within the housing, wherein the filter assemblycomprises a tube disposed in the channel and a cap disposed in at leasta portion of the cavity; mounting a header, comprising a sensingelement, in the cavity opposite the cap; tuning the pressure transducerassembly to a desired dampening frequency by sliding the filter assemblywithin the housing closer or further away from the sensing element; andfixing the filter assembly in place.